A solar pond power plant comprises two major elements: a solar pond for collecting and storing solar radiation incident on the pond, and a power plant that utilizes a low-temperature turbogenerator for converting heat extracted from the pond into electricity.
One form of solar pond comprises an upper, convective wind-mixed layer of from 3-5% salinity exposed to solar radiation, a non-convective intermediate halocline whose salinity increases with depth to a maximum of about 25-30% salinity for absorbing heat from solar radiation passing through the wind-mixed layer, and a lower heat storage layer of 25-30% uniform salinity. In Southern California and comparable latitudes, the heat transferred by conduction to the heat storage layer averages about 40 watts/m.sup.2 (on a 24-hour, yearly basis) so that a 60-acre pond is adequate to provide heat for a power plant capable of producing 5 MW peak power about four hours per day. If the heat storage layer were to reach a temperature of 80.degree. C., the heat storage layer would be from 2-3 m deep. The wind-mixed layer is from 20-50 cm, depending on weather conditions and the efficiency of windbreaks at the surface, and the halocline is about 1-1.5 m.
A suitable low-temperature turbogenerator for a solar pond power plant comprises an organic working fluid Rankine-cycle turbine that drives a generator. The power plant itself includes a boiler in the form of a heat exchanger through which hot brine from the heat storage layer is pumped, the cooled brine being returned to the heat storage layer at a point isolated from the point at which the brine is drawn into the boiler. The heat exchanger contains an organic working fluid, such as Freon or other similar fluid, which is vaporized by the hot brine in the heat exchanger; and the vaporized working fluid is supplied to a turbine within which the vaporized working fluid expands, driving a generator coupled to the turbine for generating electricity. The working fluid exhausted from the turbine is then directed to a condenser, where the working fluid is condensed and returned by pump to the heat exchanger, thus completing the working fluid cycle.
In one arrangement, the condenser is cooled by water drawn from the wind-mixed layer, the warmed water produced by the condenser being returned to the surface of the pond where the heat absorbed in the condenser is dissipated to the atmosphere. Other arrangements for the condenser are also possible, of course, where cooling water other than the pond is available.
Proper and long-term operation of a solar pond of the type described above will depend upon the degree to which the wind-mixed layer, and to a lesser extent the halocline, remain transparent to solar radiation, on the suppression of microbial activity at all levels, particularly activity that produces blooms that create internal shadows and interfere with the absorption of solar radiation, and on the extent to which the heat exchangers that act as boiler and condenser are fouled by the brine solutions being pumped therethrough.
It is, therefore, an object of the present invention to provide a method of and apparatus for treating the water of a solar power plant of the type described above such that proper and long-term operation can be achieved with a minimum of disruption to the pond.